1. Field of the Invention
The present invention relates to a watercraft propulsion system and its operating method. More specifically, it relates to a hybrid-type watercraft propulsion system having an engine and an electric motor as a source of driving force for a propeller.
2. Description of the Related Art
Japanese Publication No. 2004-257294 presents an example of a cruising method using so-called “acceleration assist,” in which the driving power of an engine is assisted by the driving power of an electric motor for the purpose of driving a power transmission device. In cruising with such acceleration assist, the output power of the electric motor is adjusted based on the operating speed of the control lever, throttle opening speed of the engine, the operating time of the control lever, and the engine rotation variation time.
This technique attempts to ensure consistency of the engine operation with the electric motor operation on the assumption that the engine is always running while under way. Therefore, such technique cannot prevent the exhaust gas and the noise emission during the trolling operation.
Japanese Publication No. 2006-036086 presents an example in which a throttle grip that can be operated in freely rotatable manner is provided on a bar handle, and a control switch is provided in the vicinity of the throttle grip. By operating the control switch, running and stopping of the engine and the electric motor, as well as the rotational direction of the electric motor, can be controlled. Also, the rotational speeds of the electric motor and engine can be adjusted according to the turning operation of the throttle grip.
However, two control means: the control switch and the throttle grip, must be used for controlling the running, stopping, and rotational speeds of the engine as well as the electric motor. Operation of such control means is troublesome.